There are two ways you can do this. You can use the longer way:
15+16+17+18+19+20+21+22+23+24 = 195 (starting from the top row, which has 15 logs, up until the bottom row, which has 24 logs, on condition that each second row has one log more than the previous one)
You can also use the formula (where n is the number of rows)
x= (n(first term+last term))/2
x= (10(15+24))/2
x= (10*39)/2
x=390/2
x=195
Either way, there are 195 logs in the stack.
The interior angles of any triangle always sum to 180°.
In the triangle, angles C and D are labeled congruent, so the missing angle has measure
180° - 2 (6x - 5)°
This angle is supplementary to the one labeled (11x + 1)°, which means
180° = (11x + 1)° + (180° - 2 (6x - 5)°)
Solve for x :
180° = (11x + 1)° + 180° - 2 (6x - 5)°
0 = (11x + 1)° - 2 (6x - 5)°
0 = (11x)° + 1° - (12x)° + 10°
(12x - 11x)° = 1° + 10°
x° = 11°
x = 11
4 x -5 = -20 then 12 + -20 = -8
Printed pages in 11 minutes = 33 pages
Printed pages in a minute = 33/11
= 3 pages/minute